A turbogenerator is used to extract energy from a gas stream such as the exhaust from a compression ignition diesel engine, the exhaust from a spark ignition gas engine, steam, an organic Rankine fluid or pressurised gas. For example, exhaust energy recovered from fluid in an exhaust conduit of a reciprocating engine may be converted into electrical power for supply to a utility electrical grid network. A turbogenerator may be provided in combination with (either in parallel or series with) a turbocharger.
In GB2451703, the operation of a series turbogenerator was described in which the speed of the turbogenerator is set to optimise its efficiency. However, in some cases efficiency may not be a primary consideration, and it may instead be desirable to optimise (as far as possible) the turbogenerator to achieve maximum power output. However, achieving such an optimisation presents a challenge.
For systems in which multiple turbogenerators are provided it is even more challenging to achieve optimal (total) power output, due to variations in the pipework between the engine and the inlets to each of the turbogenerators, and due to the fact that the amount of exhaust gases fed to the parallel turbogenerators must not cause any of the turbogenerators to exceed its individual maximum power rating. As a result, the power output from the combination of multiple turbogenerators will be limited by the one that generates the most power (for a given exhaust output from the engine).
Embodiments of the present invention seek to address these problems.